1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving signals in a mobile communication system.
2. Description of the Related Art
The rapid increase in the number of smart phone subscribers has resulted in a corresponding increase in traffic demand by those subscribers. Despite being in the process of commercialization, an Orthogonal Frequency Division Multiple Access (OFDMA)-based mobile communication system having a relatively high frequency efficiency, such as a 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) mobile communication system, will likely not have sufficient capacity to meet the increasing traffic demand. Therefore, there is a trend toward adopting a micro cell system and a repeater system to increase overall system capacity.
A configuration of a micro cell system will be described below with reference to FIG. 1.
FIG. 1 schematically illustrates a configuration of a micro cell system according to the related art.
Referring to FIG. 1, the micro cell system includes a plurality of, for example, 4 micro cells 111-1, 113-1, 115-1, and 117-1. The micro cell 111-1 is a service coverage area where a micro evolved Node B (eNB) 111-2 provides services. The micro cell 113-1 is a service coverage area where a micro eNB 113-2 provides services. The micro cell 115-1 is a service coverage area where a micro eNB 115-2 provides services. The micro cell 117-1 is a service coverage area where a micro eNB 117-2 provides services. It will be assumed that the four micro cells 111-1, 113-1, 115-1, and 117-1 have the same coverage area as the service coverage area where one macro eNB (not shown) provides services.
As described above, in the micro cell system, eNBs are installed more densely to increase the system capacity, thereby causing a decrease in the spatial coverage or size of the split cells. The decrease in the size of the split cells may contribute to increasing the average capacity that users can experience, but in inter-cell boundaries, may decrease the data capacity due to interference between data channels and increase outage probability due to interference between control channels. In addition, the smaller the cell size becomes, the more frequently User Equipments (UEs) may perform handover caused by their movements, thereby increasing overhead and making the communication environment unstable.
A configuration of a repeater system will be described below with reference to FIG. 2.
FIG. 2 schematically illustrates a configuration of a repeater system according to the related art.
Referring to FIG. 2, the repeater system includes a plurality of, for example, 4 Radio Units (RUs) 211, 213, 215, and 217 within one cell. The four RUs 211, 213, 215, and 217 transmit and receive the same signals. Therefore, in the boundaries among the RUs 211, 213, 215, and 217, signals undergo macro combining, contributing to an improvement in the capacity of UEs located in the boundary areas among the RUs 211, 213, 215, and 217, and a reduction in the outage probability. In addition, when moving between the RUs 211, 213, 215, and 217, UEs are not required to perform handover.
The repeater system is mainly used for service coverage area expansion and coverage hole filling, because it expands strong-electric field areas using multiple RUs, which are spatially separated. However, unlike the micro cell system, the repeater system may suffer from a reduction in the resource efficiency and system capacity because multiple RUs transmit and receive the same signals.
In summary, the micro cell system and repeater system may be adopted to increase overall system capacity may have the following shortcomings.
First, in the case of the micro cell system, capacities of UEs located in the inter-cell boundaries are limited, and its outage probability is relatively high. UEs may perform handover more frequently, increasing the overhead and making the communication environment unstable.
Second, the repeater system may improve capacities of UEs located in the inter-cell boundaries because multiple RUs transmit and receive the same signals, but may suffer from a reduction in the overall system capacity due to its low resource efficiency.